Method of manufacturing a multilayered doped conductor for a contact in an integrated circuit device

ABSTRACT

A method of manufacturing a memory device addressing reliability and refresh characteristics through the use of a multilayered doped conductor, and a method making is described. The multilayered doped conductor creates a high dopant concentration in the active area close to the channel region. The rich dopant layer created by the multilayered doped conductor is less susceptible to depletion from trapped charges in the oxide. This improves device reliability at burn-in and lowers junction leakage, thereby providing a longer period between refresh cycles.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.10/650,563 filed Aug. 28, 2003 now U.S. Pat. No. 6,858,534, which inturn is a division of U.S. patent application Ser. No. 10/230,948 filedAug. 29, 2002, now U.S. Pat. No. 6,670,682, issued on Dec. 30, 2003.

BACKGROUND OF THE INVENTION

The present invention relates to the field of semiconductor memorydevices, and more particularly, to a structure having improved burn-inreliability and refresh characteristics in dynamic random access memory(DRAM) devices and a method of making it.

Metal oxide semiconductor (MOS) structures are basic electronic devicesused in many integrated circuit (IC) devices. One such structure is themetal oxide semiconductor field effect transistor (MOSFET), which istypically formed in a semiconductor substrate by providing a gatestructure over the substrate to define a channel region, and by formingsource/drain regions on opposing sides of the channel region. To keeppace with the current trend toward maximizing the number of circuitdevices contained in a single chip, integrated circuit designerscontinue to design IC devices with smaller and smaller feature sizes.The current state of the art for production MOSFET devices includesphysical gate lengths of less than about 0.18 micron (μm).

To help explain problems associated with prior art MOSFET structures, across section of a typical MOSFET device is shown in FIG. 1. Inaddition, various components of device leakage current are schematicallyrepresented. The total device leakage current, I_(off), is comprised ofthree major components: device off-current I₁, gate leakage I₂, andthermal and tunneling junction leakage I₃. The device off-current I₁, isdetermined by the physical gate length L_(gate) and the channel width(W) of the device, with the gate voltage V_(g)=0 V, the drain voltage(V_(d))=power-supply voltage (V_(dd)), and the source voltage (V_(s)) toground. The gate leakage current, I₂, is determined by the gate-oxidethickness (T_(ox)), power-supply voltage (V_(dd)), and the total gatearea (L_(gate)×W). The thermal and tunneling junction leakage, I₃, isdetermined by the operating temperature of the device and the totaldoping level in the substrate, which is one reason the lightly dopedregions are typically placed adjacent the channel region in order tominimize junction leakage. The device off-state leakage current,I_(off), also known as the subthreshold leakage current, is a functionof L_(gate), temperature (T), and power-supply voltage (V_(dd)). Thesubthreshold leakage current of a MOS transistor with a physical gatelength (L_(gate)) of less than 0.18 μm exhibits what is called draininduced barrier lowering (DIBL) effect. The DIBL effect results in: (1)the leakage current changing exponentially in proportion to the drainvoltage as well as the gate voltage, and (2) with the increase in thesubstrate bias, the drain voltage dependency increases.

As the channel lengths of MOSFET devices have been reduced below 0.18μm, MOSFETS have become more susceptible to certain problems. One commonproblem is increased junction leakage I₃, which affects the refreshcharacteristics of a dynamic random access memory (DRAM) cell. DRAM is aspecific category of random access memory (RAM) containing an array ofindividual memory cells, where each memory cell includes a capacitor forholding a charge and a transistor for accessing the charge held in thecapacitor. Due to junction leakage, the stored charge must be refreshedin the capacitor on a periodic basis. Increased junction leakage leadsto a premature depletion of the capacitor's stored charge, necessitatingmore frequent refresh cycles in such DRAM devices.

Additionally, with gate lengths of less than 0.18 μm, the width of thegate overlap region (FIG. 1) in such transistors should be as small aspossible due to very tight limitations on allowable sub-thresholdleakage currents. Having a smaller gate overlap region width provides aneffective gate length that is as large as possible for a given physicalgate length, which reduces drain-induced barrier lowering. Reducingdrain-induced barrier lower improves the refresh characteristics forDRAM devices with gate overlap regions of less than 0.018 μm.

However, reducing the width of the gate overlap region is not withoutconsequences. In particular, reducing the width of the gate overlapregion worsens the reliability of the DRAM device after a high voltagestress, such as experienced during burn-in. Burn-in is the applicationof thermal and electrical stresses for inducing the failure of marginalmemory devices, those with inherent defects or defects resulting frommanufacturing aberrations which cause time and stress dependentfailures. During burn-in testing, ambient heat and the heat caused bythe current flow under the gate structure of each MOS transistor stressthe device by raising the junction temperature. This stress can lead tothe premature failure of weaker devices, as the heat of burn-in causesions in the active regions of each MOS transistor to dissipate to thepoint where the device can no longer function.

Generally, gate overlap widths greater than 0.02 μm make DRAM devicesmore robust to reliability stressing, such as burn-in testing, becausethe gate structure has control over the inversion region directlybeneath the gate structure. In such devices, the gate structure cancompensate for any charges that are trapped in the gate oxide interfacedue to the high electrical field. That is, the gate overlap regions areless likely to degrade when high voltage is applied to the device, suchas the types of voltages applied during burn-in or other manufacturingstress testing. For an NMOS device having a gate length less than 0.18μm, a gate-to-substrate voltage greater than the threshold voltage, suchas experienced during burn-in, causes the formation of an inversionlayer of free electrons (conducting channel) in the p-type substrate.Accordingly, a DRAM device with a gate overlap region width less than0.018 μm, which places the peak electric field outside the overlapregion, results in the gate structure having less control over theinversion region, thereby further degrading device lifetimesignificantly. It is to be appreciated that device lifetime is generallydefined as a percentage change in transconductance or drain saturationcurrent.

To further illustrate this point, FIGS. 13 a and 13 b, are graphs eachshowing a family of drain current (I_(d)) versus drain voltage (V_(d))characteristics for different gate voltages (V_(g)). FIG. 13 aillustrates the I_(d)/V_(d) response of a poorly designed device, whichshows degradation (i.e., low I_(d)) after the first V_(g) sweep and isone of the main reasons for failure at burn-in. FIG. 13 b, on the otherhand, illustrates well-behaved I_(d)/V_(d) curves for all V_(g) sweeps.

As mentioned previously, to reduce junction leakage DRAM devices areoften designed so that their source/drain regions have a minimum dopantdensity. However, a lightly doped source/drain region is easy to depleteeven with a small trapped-charge density at the gate oxide interface.Accordingly, device reliability decreases further in devices with gateoverlap region widths less than 0.018 μm by increasing the thresholdvoltage and transconductance after a high voltage stress, such as adevice is subjected to during burn-in.

Further aggravating the problems associated with such devices withreduced overlap gate regions, is BPSG poisoning and access devicen-sheet resistance. Rich BPSG (boron-phosphosilicate glass) layers areneeded for easy re-flow and planarity in the device. This isparticularly important in stacked DRAM cell technology where the DRAMcapacitor is formed in a very tall stack above the silicon substrate.Thin nitride or TEOS liners are needed for better contact processing,such as for forming precisely sized plug openings. However, TEOS linerscan potentially increase the trapped states and interfacial chargedensity close to the source/drain regions. TEOS liners that reduce theinterfacial oxide layer (gate oxide plus reoxidation) thickness in NMOSdevices can permit boron from a BPSG layer to diffuse through the thinTEOS liner to compensate the n-type dopant in a source/drain region.This type of diffusion increases the n-sheet resistance of the accessdevice. Such diffusion also decreases device reliability due to hotcarriers in compensated regions now having additional states to occupy,thereby further depleting the electron density in the active area of thedevice.

Accordingly, for DRAM devices having MOSFETs with gate lengths less than0.18 μm and gate overlaps less than 0.018 μm, there is a continueddesire in the industry to improve both the device burn-in reliabilityand the refresh characteristics of such devices. Improving devicereliability during burn-in will increase the overall production yieldsfor such devices, thereby reducing costs and waste. Improving devicerefresh characteristics by providing a longer refresh cycle, reduces theoverhead required to use such DRAM device, and frees up resources thatcan be expended in other device operations.

SUMMARY OF THE INVENTION

A memory device addressing reliability and refresh characteristicsbeyond that obtainable from prior art devices, as well as a method offabricating such a device is described. In particular, the presentinvention addresses reliability in memory IC devices at burn-in, suchfor example DRAMs, having gate lengths less than 0.18 μm and a gateoverlap less than 0.018 μm through the use of a multilayered dopedconductor. The multilayered doped conductor creates a high dopantconcentration in the active area close to the channel region. Becausedevice degradation is due, at least in part, to increased trap statesclose to the channel region, the rich dopant layer created by themultilayered doped conductor is less susceptible to depletion of trappedcharges in the oxide. This addresses device reliability at burn-in andlowers junction leakage, thereby permitting a longer period betweenrefresh cycles.

In particular, the present invention in one embodiment discloses anintegrated circuit semiconductor device having a substrate with a firstsurface provided with a gate structure formed thereon. Source/drainregions of the substrate have a first portion with a first dopant at afirst dopant concentration on opposite sides of the gate structure. Aconductor is provided adjacent the gate structure contacting one of thesource/drain regions. The conductor comprises a first conductive layerhaving a second dopant at a second dopant concentration, and a secondconductive layer having a third dopant at a third dopant concentrationformed on the first conductive layer.

The present invention in another embodiment discloses an integratedcircuit device having a gate electrode overlying a gate oxide layer on asurface of a semiconductor substrate, an oxide layer lying on a surfaceand sidewalls of the gate electrode, and spacers on sidewalls of theoxide layer. Lightly doped source/drain regions lie within thesemiconductor substrate on opposite sides of the gate electrode andextend at least partially beneath the sidewalls of the oxide layerforming an overlap region. A conductor is provided adjacent one of thespacers contacting one of the source/drain regions. The conductorcomprises a first conductive layer having a first dopant at a firstdopant concentration, and a second conductive layer having a seconddopant at a second dopant concentration formed on the first layer. Thefirst dopant diffusivity is less than the second dopant. The firstdopant forms a shallow diffusion region in the one of the source/drainregions beneath the conductor, and the second dopant forms a gradeddopant concentration in the one of the source/drain regions below andadjacent the shallow diffusion region.

The present invention in still another embodiment discloses anintegrated circuit device comprising a gate electrode overlying a gateoxide layer on a surface of a semiconductor substrate, an oxide layerlying on a surface and sidewalls of the gate electrode, and spacers onsidewalls of the oxide layer. Lightly doped source/drain regions areprovided within the semiconductor substrate on opposite sides of thegate electrode extending partially underneath the sidewalls of the oxidelayer to form an overlap region. Pocket implants are provided underlyingthe lightly doped source/drain regions in the semiconductor substrate.Heavily doped source/drain regions are provided lying within thesemiconductor substrate adjacent to the lightly doped source/drainregions. The device further includes a conductor provided adjacent oneof the spacers, which at least partially contacts one of the lightlydoped source/drain regions. The conductor comprises a first conductivelayer having a first dopant at a first dopant concentration, and asecond conductive layer having a second dopant at a second dopantconcentration formed on the first conductive layer. The first dopantdiffusivity is less than the second dopant, and forms a shallowdiffusion region in the source/drain regions beneath the conductor. Thesecond dopant forms a graded dopant concentration in the lightly dopedsource/drain region below and adjacent the shallow diffusion region.

The present invention in yet another embodiment discloses a DRAM devicehaving a buried capacitor memory bit cell including a substrate having afirst surface, a gate structure formed on the first surface. The gatestructure comprises a wordline. Lightly doped source/drain regions areformed within the substrate on opposite sides of the gate structure, anda conductor is provided adjacent the gate structure contacting one ofthe lightly doped source/drain regions forming a portion of a storagenode. The conductor comprises a first conductive layer having a firstdopant at a first dopant concentration, and a second conductive layerhaving a second dopant at a second dopant concentration formed on thefirst conductive layer.

The present invention in a further embodiment discloses a DRAM devicehaving a buried digitline memory bit cell including a substrate having afirst surface, a gate structure formed on the first surface. The gatestructure comprises a wordline. Lightly doped source/drain regions areformed within the substrate on opposite sides of the gate structure, anda conductor is provided adjacent the gate structure contacting one ofthe lightly doped source/drain regions forming a portion of a storagenode. The conductor comprises a first conductive layer having a firstdopant at a first dopant concentration, and a second conductive layerhaving a second dopant at a second dopant concentration formed on thefirst conductive layer.

The present invention in another embodiment discloses a processor-basedsystem comprising a processor, and an integrated circuit semiconductordevice coupled to the processor. The integrated circuit semiconductordevice comprises a substrate having a first surface, and a gatestructure formed on the first surface. Source/drain regions are formedwithin the substrate on opposite sides of the gate structure, whereineach of source/drain regions comprise a first portion having a firstdopant at a first dopant concentration. The device further includes aconductor provided adjacent the gate structure contacting one of thesource/drain regions. The conductor comprises a first conductive layerhaving a second dopant at a second dopant concentration, and a secondconductive layer having a third dopant at a third dopant concentrationformed on the first conductive layer. The second dopant diffusivity isless than the third dopant, wherein the second dopant forms a shallowdiffusion region in the source/drain region beneath the conductor. Theshallow diffusion region has a fourth dopant concentration greater thanthe first dopant concentration. The third dopant provides a gradeddopant concentration in the source/drain region below and adjacent theshallow diffusion region.

The present invention in another embodiment discloses a method offabricating an integrated circuit device. The method comprises providingan opening in an insulating layer of a partially completed device to alightly doped diffusion region. A conductor is provided in the openingand in contact with the lightly doped diffusion region. The conductorhas a first conductive layer with a first dopant and a first dopantconcentration, and a second conductive layer on the first conductivelayer. The second conductive layer has a second dopant at a seconddopant concentration.

The present invention in another embodiment, further disclosures amethod of fabricating an integrated circuit device. The method comprisesproviding a layer of a field oxide over the surface of a semiconductorsubstrate, forming a gate electrode overlying the field oxide layer, andforming a capping layer having sidewalls on the surface and sidewalls ofthe gate electrode. The method includes implanting a first ion with afirst dosage at a first energy sufficient to penetrate through the fieldoxide layer and into the substrate to form lightly doped source/drainregions in the semiconductor substrate adjacent the gate electrode.Spacers are then formed on sidewalls of the capping layer. An insulatinglayer is provided over the surface of the substrate. The method furtherincludes providing an opening through the insulating layer to one of thelightly doped source/drain regions, and providing a first conductivelayer in the opening and in contact with the one of the lightly dopedsource/drain regions. The first conductive layer has a first dopant anda first dopant concentration. A second conductive layer is provided onthe first conductive layer. The first and second conductive layers forma conductor adjacent the spacer. The second conductive layer has asecond dopant at a second dopant concentration. The first dopantdiffusivity is less than the second dopant, wherein the first dopantforms by solid-state diffusion a shallow diffusion region in the lightlydoped source/drain region beneath the conductor. The shallow diffusionregion has a dopant concentration greater than the lightly dopedsource/drain region. The second dopant provides a graded dopantconcentration in a portion of the lightly doped source/drain regions bydiffusing below and adjacent the shallow diffusion region. The methodincludes continued processing to form the integrated circuit device.

In still another embodiment, a conductor for a semiconductor substrateis disclosed. The conductor comprises a first conductive layer on thesemiconductor substrate, a first dopant within the first layer, a secondconductive layer adjacent the first layer, and a second dopant withinthe second layer.

These and other features and advantages of the invention will be morefully understood from the following description of some embodiments ofthe invention taken together with the accompanying drawings. It is notedthat the scope of the claims is defined by the recitations therein andnot by the specific discussion of features and advantages set forth inthe present description.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description of the embodiments of the presentinvention can be best understood when read in conjunction with thefollowing drawings, where like structure is indicated with likereference numerals, and in which:

FIG. 1 is a cross section view of a typical MOSFET showing off-currentleakage components;

FIGS. 2–8 are diagrams showing, in cross-section, some of the majorsteps in the manufacture of a semiconductor integrated circuit device inaccordance with various embodiments of the present invention;

FIG. 9 is a buried capacitor memory bit cell cross section formed inaccordance with the present invention;

FIG. 10 is a buried digitline memory bit cell cross section formed inaccordance with the present invention;

FIG. 11 is a block diagram of a DRAM device including a memory deviceformed in accordance with the present invention;

FIG. 12 is block diagram of a processor-based system including a memorydevice formed in accordance with the present invention; and

FIGS. 13 a and 13 b, are graphs each showing a family of drain current(I_(d)) versus drain voltage (V_(d)) characteristics for different gatevoltages (V_(g)).

The figures representing portions of an integrated circuit are not drawnto scale, but instead are drawn to illustrate features of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A sub-micron semiconductor device addressing burn-in reliability andrefresh characteristics and methods of fabricating such a device aredescribed. The device includes a MOS transistor having two-layer dopedpolysilicon plug. In the following description, numerous specificdetails are set forth such as specific materials, reticle patterns,dimensions, etc. in order to provide a thorough understanding of thepresent invention. It will be obvious, however, to one skilled in theart that these specific details need not be employed to practice thepresent invention. In other instances, known materials or methods arenot described in detail to avoid unnecessarily obscuring the presentinvention.

Additionally, it should be noted that the process steps and structuresdescribed below do not form a complete process flow for manufacturingintegrated circuits. The present invention can be practiced inconjunction with integrated circuit fabrication techniques currentlyused in the art, and only so much of the commonly practiced processsteps are included as are necessary for an understanding of the presentinvention.

Furthermore, no particular order is required for the method stepsdescribed below, with the exception of those logically requiring theresults of prior steps, for example formation of spacers 32 adjacent tothe sidewalls of the gate structure 22 logically requires the priorformation of the gate structure and its sidewalls. Otherwise, enumeratedsteps are provided below in an exemplary order which may be altered, forinstance the several ion implant steps may be rearranged using maskingand etching steps as are known in the art.

Moreover, it should be noted that although the following describedembodiments showing only the N-channel metal oxide field effecttransistor (MOSFET) portion of a CMOS integrated circuit device forpurposes of reducing complexity of illustration, other arrangements ofp-type wells, n-type wells, and combinations of the two with manydifferent doping levels may be used and still preserve the essence ofthe present invention. Moreover, it is well understood by those skilledin the art that the P-channel portion of a CMOS integrated circuitdevice can be formed by simply substituting opposite polarities to thosegiven for the N-channel embodiments.

Referring to FIG. 2, a semiconductor substrate fragment at an earlyprocessing stage is indicated generally by reference numeral 10. Theprocess begins with shallow trench isolation of substrate 10, which canbe any semiconductor material, including, for example, gallium arsenide(GaAs), silicon (Si), strained silicon, germanium (Ge),silicon-germanium (SiGe), silicon-on-insulator (SOI),silicon-on-sapphire (SOS), doped and undoped semiconductors, epitaxiallayers of silicon supported by a base semiconductor foundation, andother semiconductor structures.

Field oxide regions 12 are formed to isolate active areas in whichsemiconductor devices, such as a transistor, can then be provided in themesas according to the following processes. In the illustratedembodiment, substrate 10 is a p-type silicon substrate, and the fieldoxide regions 12 are made of a thermal oxide film having a thickness offrom about 2000 to about 5000 Angstroms. The surface of the substrate 10is thermally oxidized to form the desired gate oxide 14 thickness. Thethickness of gate oxide 14 may be from about 30 to about 200 Angstroms.

A polysilicon or polycide layer 16 is deposited, for example, bylow-pressure chemical vapor deposition (LPCVD), to a thickness of frombetween about 1000 to about 4000 Angstroms. A higher conductivitysilicide layer 18 is formed over the polysilicon or polycide layer 16 toa thickness of from between about 300 to 600 Angstroms, resulting in thestructure illustrated in FIG. 2.

Referring to FIG. 3, a layer of photoresist (not shown) is applied overthe silicide layer 18 and patterned to form a photoresist mask wheregate electrodes and/or interconnecting lines are to be formed. The gateoxide 14, the polysilicon or polycide layer 16, and the silicide layer18 are etched away in areas not covered by the mask. An insulatingcapping layer 20 is then grown or deposited on the top and sidewalls ofthe remaining layers 14, 16, and 18 to a thickness of between from about100 to about 200 Angstroms, forming gate structure 22. Capping layer 20may be a silicon nitride or other insulating material, such that gatestructure 22 functions as a word line in a DRAM cell.

The substrate then undergoes a re-oxidation to re-grow field oxide 14R,wherein gate oxide 14 in the gate structure 22 is the gate oxide. Next,lightly doped source and drain (LDD) regions are formed in the substrate10 adjacent the channel region. The lightly doped drain (LDD) N-regionsare formed by implanting ions 24, selected from phosphorus, arsenic, andantimony ions, at energies within ranges that are conventional in theart to achieve a selected source and drain impurity ion amount.

Typically, ions are implanted with dosages of from between about 1×10¹³to 1×10¹⁴ atoms/cm2 at energies of between about 5 to 80 KeV at avertical angle to provide an average dopant concentration for the LDDregions ranging from about 1×10¹⁷ ions/cm³ to 1×10¹⁹ ions/cm³. The ionimplantation forms lightly doped N-regions 26A and 26B, on respectivesides of the gate structure 22, as illustrated in FIG. 4. For LDDP-regions, boron, boron bifluoride (BF₂), or borane (B₂H₁₀) ions areused.

Referring to FIG. 4, a small pocket of a dopant concentration mayoptionally be implanted on one or both sides of the gate structure 22 byP− ions 28. In the illustrated embodiment, boron, BF₂, or B₂H₁₀ ions areimplanted with dosages of between about 1×10¹³ to 1×10¹⁴ atoms/cm² atenergies higher than those used for the LDD implantation, at betweenabout 60 to 120 KeV, and at a tilt angle of between about 0° to about40°. The pockets 30A and 30B are illustrated in FIG. 5, which arecounter-dopants only in the small critical region around the LDD regions26A and 26B. Pockets 30A and 30B effectively suppress the highelectrical field regions that cause punch-through.

A material layer is then deposited and partially etched away to leavespacers 32A and 32B on the sidewalls of the gate structure 22, as shownin FIG. 5. The spacers 32A and 32B may have a base width from about 100to about 500 Angstroms, and comprise silicon oxide, silicon nitride, orany other suitable spacer material.

Next, heavily doped source and drain (HDD) regions may optionally beformed by the ion implantation of N+ ions 34. Ions selected fromphosphorus, arsenic, antimony ions and the like are implanted atenergies within ranges that are conventional in the art to achieve aselected source and drain impurity ion amount. Typically, N+ ions areimplanted at dosages of between about 1×10¹⁴ to about 8×10¹⁵ atoms/cm²,and at energies of between about 5 to about 80 KeV at a vertical angleto provide an average dopant concentration for the diffusion regionsranging from about 1×10¹⁷ ions/cm³ to 1×10¹⁹ ions/cm³. For HDD P+regions, boron, boron bifluoride (BF₂), or borane (B₂H₁₀) ions are used.

Heavily doped regions 36A and 36B are shown in FIG. 6. Spacers 32A and32B prevent the second implant from diffusing beneath the gate structure22, which helps in the formation of the individual diffusion regions26A, 26B, 36A, and 36B.

As illustrated, a portion of each LDD region 26A and 26B slightlydiffuse below the gate structure 22, which is referred to as the gateoverlap region 38. Although the width of the gate overlap region is lessthan about 0.018 μm, the present invention addresses the problemsassociated with having gate overlap regions less than 0.018 μm found inthe prior art, through the use of a two-layer doped conductor. Thetwo-layer doped conductor according to the present invention forms ahigh dopant concentration in the source/drain regions close to theirrespective spacers 32A and 32B. A high dopant concentration in thesource/drain regions proximate to each spacer is less susceptible todepletion by trapped charges in the gate oxide 14, thereby reducingjunction leakage and also improving the refresh capabilities of DRAMdevices.

Referring to FIG. 7, formation of the two-layer doped conductoraccording to the present invention occurs at least after spacerformation, as the pocket implantation and the HDD region implant areoptional to the formation of a DRAM device. After spacer formation (andother option known fabrication processes), the substrate 10 is annealed,for example, at a temperature of between about 850° C. to about 1100° C.for between about 0.2 to about 30 minutes, to drive out any impurities.An insulating layer 40, such as BPSG, is then deposited over the surfaceof the substrate 10. Contact openings, such as opening 42, are madethrough the insulating layer 40 to the underlying semiconductor devices,such as to LDD region 26B. The width of each contact opening is fromabout 0.10 Φm to about 0.12 Φm.

It is to be appreciated that with a contact opening 42 of slightly lessthan 0.11 Φm, and in embodiments using an undoped polycrystallinematerial with a grain size slightly larger than about 0.1 Φm to fill theopening, means in essence, that about one grain of the undopedpolycrystalline material typically contacts the active area beneath theconductor. Additionally, dopants tend to segregate in the grainboundaries in the polycrystalline material. Furthermore, dopants tend tohave higher diffusion in the grain boundaries than inside the grains.Accordingly, providing a doped polycrystalline material in accordancewith the present invention, such as for example with arsenic, tends tohave a smaller grain size, thereby providing more grains in contact withthe active areas than with an undoped polycrystalline material. Sincemore grains are in contact with the active area beneath the dopedconductor of the present invention, the out-diffusion of the dopant fromthe doped conductor creates a very highly doped, very shallow dopantregion beneath the conductor, as will be explain in greater detailhereafter with references made to FIGS. 8 a and 8 b.

FIGS. 8 a and 8 b are enlarged fragmented views of the variousembodiments of a multilayered doped conductive element or conductor,such as a plug, capacitor bottom plate, digitline contact, active areacontact, and the like, formed according to the present invention. In oneembodiment, after contact opening formation, about 100 to about 1000Angstroms of a first conductive material is deposited with a firstdopant in-situ to form a first doped conductive layer 44 in contact withLDD region 26B, which also lines or blankets at least the bottom portionof contact opening 42. The conductive material may be a semiconductor orcrystalline material such as, for example, polysilicon, SiGe, and thelike, that is doped or otherwise modified so that it may exhibitconductivity.

Next, a second conductive material is deposited with a second dopantin-situ to a thickness of about 2000 to about 2500 Angstroms on thefirst doped conductive layer 44, filling contact hole 42 with a seconddoped conductive layer 46. In one embodiment, first and second dopedconductive layers 44 and 46 form a two-layered doped conductor 48. Thisembodiment of the invention is illustrated in FIG. 8 a. In otherembodiments, first and second doped conductive layers 4 and 46 may froma conductor, conductive element, or conductive component of anintegrated circuit such as, for example, as illustrated by FIGS. 9 and10, a bottom plate of a storage node 56 and/or digitline contact 58.

In another embodiment, the first conductive material is deposited incontact opening 42 to a thickness of from about 100 to about 1000Angstroms, which is then implanted with the first dopant to form thefirst doped conductive layer 44. The first dopant is implanted atdosages of between about 1×10¹⁴ to about 1×10¹⁶ atoms/cm², and atenergies of between about 1 to about 15 KeV at a vertical angle. Thefirst doped conductive layer 44 has an average dopant concentration forranging from about 1×10¹⁹ ions/cm³ to about 1×10²¹ ions/cm³.

Next, the second conductive material is deposited on the first dopedconductive layer 44 to a thickness of from about 2000 to 2500 Angstroms,which is then implanted with the second dopant to form the second dopedconductive layer 46. The second dopant is implanted at dosages ofbetween about 1×10¹⁴ to about 1×10¹⁶ atoms/cm², and at energies ofbetween about 1 to about 15 KeV at a vertical angle. The second dopedconductive layer 46 has an average dopant concentration ranging fromabout 1×10¹⁹ ions/cm³ to about 1×10²¹ ions/cm³. In another embodiments,providing layers 42 and 44 may be according to a combination of theabove-mentioned embodiments (e.g., in situ, doping, and combinationsthereof).

In still another embodiment, the first conductive material can be eitherdeposited with the first dopant in situ or later implanted as previouslydescribed above, to form the first doped conductive layer 44. Next, thefirst doped conductive layer 44 undergoes a selective dry etch to form alayer at the bottom of the contact opening 48, as illustrated in FIG. 8b, which does not line opening 42. In other embodiments, this selectivedry etch can also be used to remove most of the sidewall 32B (indicatedby dashed lines) in order to create a larger opening for the depositionof the second conductive layer, if desired. After dry etching, thesecond conductive material is then deposited with the second dopant insitu or later implanted as also previously described above to form thesecond doped conductive layer 46, and thereby forming the two-layerdoped conductor 48.

In the dry etching embodiments, it is to be appreciated that the firstconductive layer is deposited at a slightly larger thickness (about 15%larger) first to account for material removal during etch in order tohave a final thickness of from about 2000 to 2500 Angstroms.

In still another embodiment, the first conductive material may bedeposited without being doped insitu or implanted before the secondconductive material is provided. In such an embodiment, after the secondconductive material is provided, the first conductive layer receives itsdopant by way of diffusion or implantation through the second conductivelayer 46 with dosages and energies to achieve the above-mentionedconcentration for the first doped conductive layer 44.

In the preferred embodiments, the first dopant diffusivity is less thanthe second dopant, such that a dopant-type diffusion region 50 is formedunder the conductor 48 in a portion of LDD region 26B. This is due tosolid-source diffusion from the first doped conductive layer 44 to LDDregion 26B. Diffusion region 50 is very shallow, extending under theconductor 48 to a depth of no greater than about 0.02 μm into LDD region26B. Further, diffusion region 50 extends partially under spacer 32B,but not beyond LDD region 26B. It is to be appreciated that bysolid-source diffusion, the dopant concentration of the shallowdiffusion region 50 is greater than the dopant concentration in LDDregion 26B.

Moreover, because the second dopant has a higher diffusivity than thefirst dopant, the second dopant will also out diffuse from the seconddoped conductive layer 46 through the first doped conductive layer 44,and into the LDD region 26B. Accordingly, the second dopant will outdiffuse beyond the shallow diffusion region 50 to provide, to someextent, a graded dopant concentration portion 52 to the junction betweenthe spacer 32B, the LDD region 26B, and the shallow dopant-type region50. As illustrated, the portion 52 also extends partially under thespacer 32B, but not beyond the LDD region 26B.

For NMOS, the first dopant is arsenic, antimony, or combinationsthereof, and the second dopant is phosphorous. For PMOS, the firstdopant may be boron and the second dopant BF₂ or vice-versa. By theabove-described method of forming a multilayered doped conductor, devicedegradation due to increased trap states in the channel region can bemitigated. Several types of exemplary semiconductor integrated circuitdevices employing the principles of the present invention will bedescribed hereafter.

After conductor formation according to the methods of the presentinvention, the integrated circuit may be completed according to knownfabrication methods. For example, in one embodiment, the structure maybe completed to form a pair of DRAM memory cells, such as illustrated inFIGS. 9 and 10.

FIG. 9 is a process cross section for a pair of buried capacitor memorybits 53, which places a digitline 54 physically above a storagecapacitor 56. The digitline 56 is constructed from metal, silicidedpolysilicon, polycided polysilicon and combinations thereof. Thedigitline contact 58 is formed using metal, polysilicon, or a two-layerdoped conductor of the present invention, such as illustrated. Thestorage capacitor 56 is formed with the two-layer doped conductor 48 ofthe present invention as the bottom plate, an oxide-nitride-oxide (ONO)dielectric 60, and a sheet of polysilicon 62 which forms the common nodeor cell plate shared by all memory bit capacitors. The capacitor shapecan be simple, such as a rectangle, or complex, such as concentriccylinders or stacked discs.

Additionally, the two-layer doped conductor 48 may be used in the otherbasic memory bit configuration used in the DRAM art, such as isillustrated in FIG. 10, which shows a pair of capacitor over bitlinecells 64. Such memory bit configurations are useful in forming a numberof different memory array designs, such as 8F² and 6F², which aredisclosed in greater detail by commonly assigned U.S. Pat. No.6,392,303, the disclosure of which is incorporated fully by reference,and which memory array designs may advantageously be improved with thetwo-layer doped conductor of the present invention.

Such memory bit arrays having a two-layer doped conductor 48 of thepresent invention, may further be provided in a DRAM device 100, whichis illustrated in FIG. 11. DRAM device 100 includes a memory array 102which employs a plurality of MOS transistors 53 or 64 (FIGS. 9 and 10,respectively) formed with a plurality of two-layer doped conductorsaccording to the present invention in order to prevent electrical chargefrom leaking out of an associated data storage capacitor. The remainingDRAM components are formed according to known fabrication methods. TheDRAM device 100 as illustrated, further includes an I/O circuit 104,standby controller 106, and word driver 108, which are designed tooperate with power supply voltages Vcc2, Vpp that are higher than Vcc1.For drive of the memory-cell transistors 102, word lines W are arrangedto carry and handle large amplitude voltage signals from word driver108.

The DRAM device 100 further includes row and column decoders 110 and112, and address buffers 114 and 116. Decoders 110, 112 and addressbuffers 114, 116 handle small amplitude signals for drive by the lowvoltage Vcc1, supra. A sense amplifier 118 is designed to operatevoltages sensed from bit line B that are higher than power supplyvoltage Vdd.

When input circuit 104 receives at its input an address signal Ai, whichis as great as Vcc2 in amplitude, this input signal is level-convertedinto a small Vcc1 amplitude signal, which is then passed to addressbuffers 114, 116 and decoders 110, 112. Although not visible in FIG. 11,row decoder 110 contains therein a level converter for converting theVcc1 amplitude signal into an amplitude-increased signal (Vpp), which isthen supplied to word driver 108. The column address YS is sent to thesense amplifier 118, which depending on the current operation the memorycell, will take on the state of the applied voltage. If a readoperation, the sense amplifier 118 provides the sensed voltage signal ofthat memory to a main amplifier 120, which is then provided to outputcircuit 122. The sensed signal is amplified via power supply voltagesVcc1 and Vcc2.

A further embodiment of the invention is shown in FIG. 12, whichillustrates a block diagram of a processor-based system 200 utilizing aDRAM memory circuit 208 constructed in accordance with the presentinvention. That is, the memory circuit 208 utilizes one of the MOSFETmemory arrays 53 (FIG. 9) or 64 (FIG. 10) constructed in accordance withthe present invention (FIGS. 1 to 8). The processor-based system 200 maybe a computer system, a process control system, or any other systememploying a processor and associated memory. The system 200 includes acentral processing unit (CPU) 202, e.g., a microprocessor, whichcommunicates with the DRAM memory circuit 208 and an I/O device 204 overa bus 220. It must be noted that the bus 220 may be a series of busesand bridges commonly used in a processor-based system, but forconvenience purposes only, the bus 220 has been illustrated as a singlebus.

A second I/O device 206 is illustrated, but is not necessary to practicethe invention. The processor-based system 200 also includes a read-onlymemory (ROM) circuit 210 and may include peripheral devices such as afloppy disk drive 212 and a compact disk (CD) ROM drive 214 that alsocommunicates with the CPU 202 over the bus 220 as is well known in theart. It should be noted that the CPU 202 could be combined on a singlechip with one or more DRAM memory circuits 208 and ROM circuits 210.

While the invention has been described in detail in connection with anumber of various embodiments known at the time, it should be readilyunderstood that the invention is not limited to such disclosedembodiments. Rather, the invention can be modified to incorporate anynumber of variations, alterations, substitutions or equivalentarrangements not heretofore described, but which are commensurate withthe spirit and scope of the invention. Accordingly, the invention is notto be seen as limited by the foregoing description, but is only limitedby the scope of the appended claims.

1. A method of fabricating a memory integrated circuit device having achannel region less than 0.18 μm and a gate overlap less than 0.018 μm,comprising: forming a gate electrode overlying a layer of field oxideover the surface of a semiconductor substrate; forming a capping layerhaving sidewalls on the surface and sidewalls of said gate electrode;providing lightly doped source/drain regions in said semiconductorsubstrate adjacent said gate electrode; forming spacers on sidewalls ofsaid capping layer; providing an insulating layer over the surface ofsaid capping layer of said gate electrode and over the surface of saidsubstrate; providing an opening through said insulating layer to one ofsaid lightly doped source/drain regions; providing a conductor for saidsemiconductor substrate; and continuing processing to form said memoryintegrated circuit device.
 2. The method of claim 1, wherein saidconductor for said semiconductor substrate comprises: a first conductivelayer on said semiconductor substrate; a first dopant within said firstconductive layer; a second conductive layer adjacent said firstconductive layer; and a second dopant within said second conductivelayer.
 3. The method of claim 2, wherein said first conductive layer isin said opening and in contact with said one of said lightly dopedsource/drain regions.
 4. The method of claim 2, wherein said firstconductive layer has a first dopant concentration.
 5. The method ofclaim 2, wherein said first and second conductive layers form saidconductor adjacent one of said spacers.
 6. The method of claim 2,wherein said second conductive layer has a second dopant concentration.7. The method of claim 2, wherein said first dopant diffusivity beingless than said second dopant, said first dopant forming by solid statediffusion a shallow diffusion region in said one of the lightly dopedsource/drain regions beneath said conductor having a dopantconcentration greater than said one of the lightly doped source/drainregions, and said second dopant providing a graded dopant concentrationin a portion of said one of the lightly doped source/drain regions bydiffusing below and adjacent said shallow diffusion region.
 8. Themethod of claim 7 wherein said shallow diffusion region diffusespartially beneath said one of said spacer.
 9. The method of claim 2further comprising a doped region of the substrate under the firstconductive layer.
 10. The method of claim 9 further comprising a gradeddoped region of the substrate under said doped region.
 11. The method ofclaim 9 wherein said doped region extends under the conductor to a depthof no greater than about 0.02 μm.
 12. The method of claim 9 wherein saiddoped region extends partially under a spacer provided adjacent saidtransistor.
 13. The method of claim 9 wherein a dopant concentration ofsaid doped region concentration is greater than a dopant concentration alightly doped region of said substrate.
 14. The method of claim 2,wherein said conductor is located adjacent a transistor.
 15. The methodof claim 2, wherein said conductor has a thickness of about 100 to about1000 Angstroms for the first conductive layer.
 16. The method of claim2, wherein said conductor has a thickness of about 2000 to about 2500Angstroms for the second conductive layer.
 17. The method of claim 2wherein said first conductive layer lines a contact opening.
 18. Themethod of claim 2 wherein said first conductive layer has an averagedopant concentration for ranging from about 1×10¹⁹ to about 1×10²¹ions/cm³ of said first dopant.
 19. The method of claim 2 wherein saidsecond conductive layer has an average dopant concentration ranging fromabout 1×10¹⁹ to about 1×10²¹ ions/cm³ of said second dopant.
 20. Themethod of claim 2 wherein said first dopant diffusivity is less thansaid second dopant.
 21. The method of claim 2, wherein said first dopantcomprises arsenic, antimony, or combinations thereof, and said seconddopant comprises phosphorus.
 22. The method of claim 2, wherein saidfirst dopant and said second dopant each comprises boron, boronbifluoride, borane, or combination thereof.
 23. A method of fabricatinga memory integrated circuit device having a channel region less than0.18 μm and a gate overlap less than 0.018 μm, said method comprising:providing a layer of a field oxide over the surface of a semiconductorsubstrate; forming a gate electrode overlying a layer of field oxide;forming a capping layer having sidewalls on the surface and sidewalls ofsaid gate electrode; providing lightly doped source/drain regions insaid semiconductor substrate adjacent said gate electrode; formingspacers on sidewalls of said capping layer; providing an insulatinglayer over the surface of said capping layer of said gate electrode andover the surface of said substrate; providing an opening through saidinsulating layer to one of said lightly doped source/drain regions;providing a conductor for said semiconductor substrate; providing ashallow, dopant portion in the semiconductor substrate adjacent to thechannel region that addresses susceptible to depletion of trappedcharges in the channel region of a semiconductor substrate; andcontinuing processing to form said integrated circuit device.
 24. Themethod of claim 23, wherein providing said conductor for saidsemiconductor substrate includes: providing a first conductive layer onsaid semiconductor substrate; proving a first dopant within said firstconductive layer; providing a second conductive layer adjacent saidfirst conductive layer; and providing a second dopant within said secondconductive layer, said second dopant diffusivity being greater that saidfirst dopant.
 25. A method of fabricating a memory integrated circuitdevice having a channel region less than 0.18 μm and a gate overlap lessthan 0.018 μm, comprising: forming a gate electrode overlying a layer offield oxide over the surface of a semiconductor substrate; forming acapping layer having sidewalls on the surface and sidewalls of said gateelectrode and in contact with said layer of field oxide; providinglightly doped source/drain regions in said semiconductor substrateadjacent said gate electrode; forming spacers on sidewalls of saidcapping layer; providing an insulating layer over the surface of saidcapping layer of said gate electrode and over the surface of saidsubstrate; providing an opening through said insulating layer to one ofsaid lightly doped source/drain regions; providing a conductor for saidsemiconductor substrate; and continuing processing to form said memoryintegrated circuit device.